The subject matter disclosed herein related to the field of chemical detection and more particularly to a chemical analysis system comprising a chemical sample collector that is operated remotely from a chemical analyzer.
In some situations, emergency response personnel need to quickly and accurately identify and quantify chemical hazards. These circumstances include both accidental discharges of toxic or industrial chemicals and deliberate releases, such as in terrorist attacks or chemical warfare. The need for rapid assessment of chemical health risks, combined with the unstable nature of many chemicals of concern, often mandate that the analysis occur at, or as near as possible to, the site of a chemical release. A number of chemical detector technologies have been developed to address potential chemical hazards that may exist in air, on surfaces, or in water. These technologies include Mass Spectrometers (MS), Gas Chromatograph/Mass Spectrometers (GC/MS), Ion Mobility Spectrometers (IMS), along with optical technologies such as Fourier Transform Infrared Spectroscopy (FTIR) and Raman, among others. Some of these technologies have been miniaturized and ruggedized to the extent that handheld analyzers can be carried directly into environments of chemical contamination. Some of these approaches are also based on small mass spectrometers (MS), as described in U.S. Pat. No. 8,525,111; U.S. Pat. No. 7,115,859; and 908devices.comitechnology/, the entirety of which are incorporated herein by reference. However, the designers of these and other miniaturized systems have often been forced to make sacrifices in analytical performance in order to minimize system size and weight. These sacrifices can negatively impact system performance, particularly in situations requiring highly definitive chemical analyses, such as forensics and attribution. Typically, miniature analyzers are too expensive for the resulting measure of analytical performance provided, and this compromise in performance is not acceptable in many emergency response scenarios. Slightly larger and higher fidelity chemical analyzers have been developed for field applications. Although these field analyzers can be moved into a contaminated hazmat area, the size, weight, and limited battery life or power requirements of these field analyzers typically leave these instruments to be stationed in safe areas just outside the contaminated zone. These include for example GC/MS analyzers such as the Bruker E2M and the INFICON HAPSITE.
In emergency response scenarios requiring a high fidelity analysis, a remote sample collector is typically transported into the contaminated hot zone to obtain a sample to be analyzed by a high performance chemical analyzer stationed in a nearby field lab. Although the analysis is delayed while the exterior of the sample collector is decontaminated, if necessary, and transported out of the hot zone, this process permits a high performance analysis under more controlled conditions than are typically possible directly at the chemical source. Systems and devices that make use of this remote sampling paradigm are taught in U.S. Pat. No. 6,167,767; U.S. Pat. No. 6,321,609 B1; U.S. Pat. No. 6,446,514; U.S. Pat. No. 5,988,002; U.S. Pat. No. 5,895,375; U.S. Pat. No. 8,146,448; U.S. Pat. No. 8,578,796; U.S. Pat. No. 7,600,439; U.S. Pat. No. 7,841,244; U.S. Pat. No. 5,859,375; U.S. Pat. No. 7,357,044; and U.S. Pat. No. 5,336,467, the entirety of which are incorporated herein by reference.
Along with the performance improvements garnered by bringing the sample to a higher performance analyzer, there are also benefits in carrying a small, lightweight, low power, and low cost sample collector. Remote sample collection affords logistical savings by allowing sample collection in multiple locations simultaneously and analyzing these samples at one nearby chemical analyzer. Despite the aforementioned advantages, chemical analysis systems employing remote sample collection suffer from performance issues related to the decoupling of collection from analysis. For example, the sample can be collected in a non-optimal time and place. Many sources, such as gas and vapor leaks, produce turbulent plumes with a high degree of spatiotemporal variability in vapor phase concentration. Because of this variation, it is possible to collect sample air near a vapor point source and still miss virtually the entire chemical sample. Even non-stochastic sources of concentration variation, such as advection, can cause a sample collector to entirely miss collection from a point source. Collecting samples in the wrong location can thus lead to incorrect determinations on site safety with respect to toxic chemicals.
In another example of a disadvantage of the decoupling between collection and analysis, an insufficient quantity of a sample can be collected even when collecting in an optimal location, if for example the collection time was too short. Collecting an insufficient quantity of a sample will often result in a low signal-to-noise ratio (SNR) in the chemical analysis and thus missed detections or incorrect identifications leading to false alarms.
In yet another disadvantage, an excess amount of a sample can be collected. Collecting excess sample can generate outcomes that are as detrimental to the quality of the chemical analysis as those that occur when collecting too little sample. GC columns, and particularly the narrow bore thin phase columns used for very high speed chromatography, have very limited capacity. Overloading the columns with excess sample causes peak broadening and decreased GC separation performance. Decreased separation performance may defeat a primary purpose of the GC column, which is to separate chemicals of interest from interfering chemicals in a background matrix. This reduces the quality of analysis, and may lead to missed detections or false alarms. Other components in the analyzer, such as the MS electron multiplier and electrometer, may also have limited dynamic range. In applications with very high speed GC separations and sharp GC peaks, fast scanning of the mass spectrometer is required to generate enough data points for accurate integrations of the MS data points collected across a GC peak. In practice, this fast scanning can result in an effective dynamic range of as little as 2 or 3 decades in a field analyzer. Thus, it is important to collect the optimal mass of sample when the sample is to be subjected to the high speed analysis desired in typical hazardous chemical scenarios.
In yet another disadvantage of existing systems, with only one opportunity to analyze a collected sample, suboptimal instrumental settings may be used to analyze a sample having a mass outside of the optimal range. These suboptimal settings can lead to a poor quality analysis with lower signal to noise ratios and reduced GC peak integration precision than which would be achieved if the components were adjusted to more optimally match the quantity of collected sample.
A further disadvantage of the decoupling of collection from analysis is that collected samples may need to be decontaminated before being removed from the hazmat hot zone and transported to the analyzer. This requires decontamination of the exterior of a sample cartridge prior to analysis. Inadequate knowledge with respect to the levels of VOCs in the hazardous sample collection environment may lead to unnecessary or inadequate decontamination procedures. Excessive decontamination procedures may even degrade some low stability chemical samples.
The HAPSITE ER (products.inficon.com/GetAttachmentaxd?attaName=b0ddf534-db3e-4920-b9c1-ec872bc28a4d) discloses a basic form of reactive sample collection. In this embodiment, the instrument makes use of the same MS that the system uses for GC/MS analysis. In a particular configuration of inlet valves, sample air from an attached sample line is pulled directly to the MS for analysis. The system informs the operator when the sample line is in an acceptable position for good sample collection, meaning that the sum of all MS ions detected for all of the volatile organic compounds (VOCs) measured by the MS are within an acceptable range. The user then switches the instrument into a sampling mode, which has a different configuration of inlet valves, and a predefined volume of sample air is collected on an internal sample collector. The system collects a volume of air rather than a predefined mass of chemical sample. If the sample vapor concentration changes during the collection interval, such as due to wind, turbulence, or slight movement of the sample line with respect to a point source, a suboptimal quantity of sample, such as too much or too little, is collected despite collection of the intended volume of air. A further disadvantage of this approach is that the entire instrument must be carried into the hot zone since the same MS is used to provide the level indication that is used for the full chemical analysis.
Another form of reactive sampling using a surface condition indicator for feedback during a sample collection is taught by U.S. Pat. No. 8,193,487, the entirety of which is incorporated herein by reference. The surface condition indicators are chemicals monitored with the MS itself during the sample collection. This technique is indicative of a surface condition such as the temperature of a contaminated soil surface rather than more directly indicative of concentrations of the target chemicals in air. This technique also uses the same MS for feedback preventing it from being used in a lightweight, low cost, remote sample collector. U.S. Pat. No. 7,992,424, the entirety of which is incorporated herein by reference, teaches adjusting instrumental parameters for a GC/MS analysis based on an estimate of the amount of a collected sample by diverting sample to a membrane inlet to the MS prior to GC analysis. This technique helps optimize the GC analysis for variations in sample quantity. However, this technique cannot be made remote from the analyzer and provides no mechanism to obtain a sample in the best location or to collect an optimal sample quantity.
Another form of reactive sample collection is described by U.S. Pat. No. 7,168,298, the entirety of which is incorporated herein by reference. A mass sensitive sample collection device includes a pivot-plate resonator with a chemically sensitive coating. During sampling, the resonator changes frequency which corresponds to a change in the total collected mass of the sample. Using the sample collection device as the detector requires that any sample detected is also collected. This approach can be disadvantageous because the system cannot scan an area for a plume or point source of contamination prior to initiating collection, which can lead to collection of excess background chemicals. Additional disadvantages with this approach are that the micro resonators are expensive relative to glass or metal tubes used for most types of field sample collection, have poorly swept geometries, meaning that they are not easily coupled to a GC system which leads to poor chromatographic peak shapes, and, by nature of the microelectromechanical systems (MEMS) design, have very limited sample capacity. In some embodiments, limited sample capacity negates the benefits from collecting an optimal amount of sample. Additionally, commonly used adsorbents for the collection of toxic industrial chemicals (TICs) and Chemical Warfare Agents (CWAs), such as graphitized carbon, are granular and do not lend themselves to forming the tightly coupled thin films required for the acoustic coupling of the adsorbent/absorbent to the resonator. Thus, the device must collect samples using inferior collection materials.